Thin film magnetic head

ABSTRACT

A magnetic material having a low coefficient of thermal expansion of 11.5×10 −6 /K or less is used for forming at least one of a lower shield or an upper shield. A laminated film comprising a layer of the magnetic material having a low coefficient of thermal expansion of 11.5×10 −6 /K or less, and an 80 wt % NiFe alloy layer, is used for forming at least one of the lower shield and the upper shield. Thus, the thin film magnetic head having reduced after-record noise and reduced thermal protrusion can be obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese application No.2003-130983, filed May 9, 2003, the disclosure of which is incorporatedby reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a thin film magnetic head usedin a disk storage device. In particular, the invention relates to a thinfilm magnetic head that achieves a low flying height suitable forhigh-density recording with high reliability.

[0004] 2. Description of Related Art

[0005] In recent years, an increase in recording density of a diskstorage device has raised demands for improvements in performance of arecording medium and developments of a thin film magnetic head excellentin write/read characteristics. At present, a head using an MR(Magnetoresistive) element or a GMR (Giant Magnetoresistive) element,both of which are capable of achieving a high read output, is used as aread head. In addition, a TMR (Tunneling Magnetoresistive) elementcapable of achieving higher read sensitivity is being developed as theread head. On the other hand, a conventional inductive thin filmmagnetic head exploiting the electromagnetic induction is used as awrite head. Also, the above-mentioned read head and write head arecombined into one magnetic head to be used as an integrated read/writethin film magnetic head.

[0006] As shown in FIG. 6 of Japanese published application JPA2001-176031, the conventional read/write thin film magnetic head isobtained by forming a lower shield 111, a read element 113, and a midshield 112 serving as an upper shield and a lower pole piece on asubstrate 103, and then forming a write gap 102 a, a thin film coil 106,an upper pole piece 114, and other components on the mid shield 112,followed by coating with an alumina protection film 115. However, asdisclosed in Japanese published application JPA 2001-176031, since awrite current tends to affect a magnetic domain of the mid shield, whichin turn affects the read element, the read output is fluctuated therebyand causes noise. Therefore, a countermeasure is proposed which reducesnoise in read output by dividing the mid shield into an upper shield 4and a lower pole piece 5 that are separated from each other with anon-magnetic layer 4 a in-between as shown in FIGS. 1 and 4 of Japanesepublished application JPA 2001-176031 so as to reduce the change inmagnetic domain of the upper shield caused by the write operation. Thiscountermeasure is currently put to practical use.

[0007] In recent years, a reduction in a head-disk space, i.e., areduction in flying height, has been attained in order to improve therecording density, but the reduction in flying height has caused aproblem known as “thermal protrusion”. This is a protrusion, due tothermal expansion of the air bearing surface of the magnetic head when adisk storage device is used in a hot environment. The thermal protrusionis caused when the metal portion having a high coefficient of thermalexpansion and organic substances such as a resist of a thin filmmagnetic head thermally expand in a hot environment, to protrude abovethe height of a substrate formed of Al₂O₃—TiC or the like having a lowcoefficient of thermal expansion at the air bearing surface. If aprominent thermal protrusion occurs, it is possible that a tip of themagnetic head comes in contact with the recording medium thereby wearingdown or damaging itself or wearing down or damaging the medium. In anactual device, since a flying height at room temperature is set to arelatively great value in order to prevent the contact in a hotenvironment, write/read characteristics tend to be deteriorated at roomtemperature or in a hot environment, which makes it very difficult toincrease recording density. Thus, in order to realize a disk storagedevice with high recording density, the thermal protrusion must beprevented.

[0008] In the conventional thin film magnetic heads, like those shown inFIGS. 1 and 4 of Japanese published application JPA 2001-176031, whereinthe upper magnetic shield does not double as the lower pole piece, NiFealloy films containing 80 wt % Ni, i.e., so-called permalloy films, aretypically used as magnetic materials for the magnetic shield. Since themagnetic materials have a low coercive force and a low magnetostrictioncoefficient, they are suitably used as magnetic materials for themagnetic shield. However, such materials have a coefficient of thermalexpansion of about 12.8×10⁻⁶/K, that is larger than that of Al₂O₃—TiC,which is 7.1×10⁻⁶/K, typically used for the substrate and Al₂O₃ used fora protection film. Therefore, a magnetic shield of a thin film magnetichead wherein an 80 wt % NiFe alloy (80 wt % Ni) film is used as themagnetic shield material protrudes above the height of the substrate atthe air bearing surface in the direction of the medium in a hotenvironment. The height of the thermal protrusion is as small as about 1nm per 10° C., but the change of 1 nm in the flying height has asignificant influence on the write/record characteristics of themagnetic storage device with high recording density. Accordingly, theincrease in flying height at room temperature to compensate for theamount of protrusion due to the temperature rise from the roomtemperature to about 60° C. leads to a considerable deterioration in thewrite/read characteristics. Therefore, if it is possible to reduce theflying height at room temperature by reducing the thermal protrusioneven slightly, there will be improvement in the write/readcharacteristics.

SUMMARY OF THE INVENTION

[0009] Embodiments of the present invention are directed to a magneticmaterial having a low coefficient of thermal expansion used for amagnetic shield.

[0010] In a preferred embodiment, a magnetic material that has acoefficient of thermal expansion lower than that of an 80 wt % NiFealloy is used for forming part or whole of a magnetic shield. A NiFealloy containing 30 to 55 wt % of Ni has a reduced coefficient ofthermal expansion as compared with that of the 80 wt % NiFe alloy. Forexample, a composition of 46 wt % NiFe provides a low coefficient ofthermal expansion of about 8.5×10⁻⁶/K. Also, such material has a softmagnetic property suitable for the magnetic shield. Therefore, it ispossible to reduce the thermal protrusion of a thin film magnetic head,if such magnetic material is used as a part or whole of the magneticshield.

[0011] Further, in another preferred embodiment of the presentinvention, at least one of a lower shield and an upper shield is alaminated film consisting of a layer formed from a 80 wt % NiFe alloyand a layer formed from a magnetic material having a low coefficient ofthermal expansion. In this case, the layer of the 80 wt % NiFe alloy isdisposed to face the read element while the layer of the magneticmaterial having the low coefficient of thermal expansion is disposedapart from the read element. As described above, the 80 wt. % NiFe alloyis characterized by low coercivity, a low magnetostriction coefficient,and an excellent soft magnetic property. On the other hand, while themagnetic material having a low coefficient of thermal expansion such asthe NiFe alloy having a composition mainly comprising 46 wt % Ni is usedfor forming a pole piece of the head, the NiFe alloy is high incoercivity and magnetostriction coefficient as compared with the 80 wt %NiFe alloy. If the material having high coercivity and a highmagnetostriction coefficient is used as the magnetic shield, an abnormalmagnetic domain structure tends to be obtained. More specifically, themagnetic domain structure is changed due to a magnetic field that flowsinto the magnetic shield when a write current is applied to the magnetichead, which makes noise in read output liable to occur. In order toprevent such phenomenon, one layer of the magnetic shield adjacent tothe read element is formed from the 80 wt % NiFe film, and the otherlayer is formed from the magnetic material having the low coefficient ofthermal expansion. Thus, it is possible to prevent noise in read outputand to reduce the thermal protrusion.

[0012] The present invention will hereinafter be described in moredetails through embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a cross-sectional view of a thin film magnetic head ofthe present invention.

[0014]FIG. 2A is a cross-sectional view of a multilayered magneticshield of the thin film magnetic head of the present invention.

[0015]FIG. 2B is a cross-sectional view of a multilayered magneticshield of the thin film magnetic head of the present invention.

[0016]FIG. 3 is a cross-sectional view of a thin film magnetic headaccording to another embodiment of the present invention.

[0017]FIG. 4 is a plan view showing a magnetic shield and a read elementof an thin film magnetic head according to another embodiment of thepresent invention.

The following table includes a description of reference numerals.

[0018]  1 substrate  2 base alumina  3 lower shield   3a lower shieldlower layer   3b lower shield upper layer  4 read gap  5 read element  6upper shield   6a upper shield upper layer   6b upper shield lower layer 7 separation layer  8 lower pole piece  9 lower pole front end layer 10lower pole back end layer 11 read gap layer 12 upper pole front endlayer 13 upper pole back end layer 14 non-magnetic insulation layer 15coil 16 coil insulation layer 17 upper pole piece 18 protection layer 19air bearing surface 20 recording medium 21 main pole piece 22 insulationlayer 23 side shield

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0019]FIG. 1 is a cross-sectional view of a thin film magnetic head of afirst embodiment. On a substrate 1 formed from a non-magnetic material,a base alumina 2 is applied so as to provide surface smoothness andelectrical insulation properties. A lower shield 3 formed from amagnetic material having low coefficient of thermal expansion isprovided on the base alumina 2 in order to improve read resolution andto eliminate influences of external magnetic fields. A read gap 4 formedof a non-magnetic insulating material is provided on the lower shield 3.A read element 5 formed of an MR element or a GMR element is disposed inthe read gap. On the read gap 4, an upper shield 6 formed from amagnetic material having low coefficient of thermal expansion isprovided. A separation layer 7 that is formed from a non-magneticmaterial is provided on the upper shield 6 to be used for separating awrite head from a read head. A write unit is formed on the separationlayer 7. The write unit 7 includes a lower pole piece 8, a lower polefront end layer 9, a lower pole back end layer 10, a write gap 11, anupper pole front end layer 12, an upper pole back end layer 13, anon-magnetic insulation layer 14, a coil 15, a coil insulation layer 16,an upper pole piece 17, and a protection layer 18.

[0020] In write operation, a write current is applied to the coil 15 toinduce a magnetic flux in the upper pole piece 17, upper pole back endlayer 13, the lower pole back end layer 10, the lower pole piece 8, thelower pole front end layer 9, and the upper pole front end layer 12, anda write magnetic field is generated from the write gap 11 so that signalmagnetization is written on a recording medium 20 that rotates with aflying height being maintained as a space between the recording medium20 and an air bearing surface 19.

[0021] In another embodiment of the present invention, a lower shield 3has a lower shield lower layer 3 a formed from a magnetic materialhaving a low coefficient of thermal expansion and a lower shield upperlayer 3 b formed from an 80 wt % NiFe alloy as shown in FIG. 2A. Inaddition, an upper shield 6 has an upper shield upper layer 6 a formedfrom a magnetic material having a low coefficient of thermal expansionand an upper shield lower layer 6 b formed from a 80 wt % NiFe alloy.

[0022] Heat deformations of the thin film magnetic head of the presentembodiment (shown in FIG. 1) and the conventional thin magnetic headwere calculated to determine those thermal protrusions. The head of thepresent embodiment has the lower shield 3 and the upper shield 6, bothof which are formed from the magnetic material having a low coefficientof thermal expansion. On the other hand, the conventional head has thelower shield 3 and the upper shield 6, both of which are formed from the80 wt % NiFe alloy. In addition, the thermal protrusion of the thin filmmagnetic head (shown in FIG. 2A) having the magnetic shields each ofwhich is the stack of layers consisting of the layer of the magneticmaterial having a low coefficient of thermal expansion and the 80 wt %NiFe alloy layer was also determined.

[0023] Materials used for the components other than the magnetic shieldswere as follows: the substrate 1 was formed from Al₂O₃—TiC; the lowerpole piece 8, the lower pole front end layer 9, the lower pole back endlayer 10, the upper pole front end layer 12, the upper pole back endlayer 13, and the upper pole piece 17 were formed from 46 wt % NiFe; theread gap 4, the separation layer 7, the write gap 11, and the protectionlayer 18 were formed from Al₂O₃; the coil 15 was formed from Cu; and thecoil insulation layer 16 was formed from photoresist. Properties of thematerials are shown in Table 1. TABLE 1 Thermal Young's Coefficient ofLinear Conductivity Modulus Poisson's Thermal Expansion Material(μW/μmK) (Gpa) Raito (10⁻⁶/K) Al₂O₃— 20 390 0.22 7.1 TiC Al₂O₃ 1.3 4100.25 7.1 80 wt % 35 200 0.3 12.8 NiFe 46 wt % 35 144 0.3 8.5 NiFephotoresist 0.5 3.7 0.35 30 Cu 403 110 0.3 16.2

[0024] The thermal protrusion per 10° C. of temperature rise at each ofthe lower shields was calculated under the above-described conditions.The calculations are shown in Table 2. TABLE 2 Conventional HeadStructure Example Example 1 Example 2 Example 3 lower shield lower 80 wt% NiFe 46 wt % NiFe 46 wt % NiFe 46 wt % NiFe layer material 2.1 2.1 0.71.4 thickness (μm) lower shield upper — — 80 wt % NiFe 80 wt % NiFelayer material 1.4 0.7 thickness (μm) upper shield lower 80 wt % NiFe 46wt % NiFe 80 wt % NiFe 80 wt % NiFe layer material 1.3 1.3 0.9 0.4thickness (μm) upper shield upper — — 46 wt % NiFe 46 wt % NiFe layermaterial 0.4 0.9 thickness (μm) protrusion 0.63 0.27 0.53 0.40protrusion ratio 1 0.43 0.84 0.63

[0025] As shown in Table 2, the thermal protrusion of the thin filmmagnetic head of Example 1 wherein 46 wt % NiFe is used in place of 80wt % NiFe for forming the magnetic shield is less than half that of theconventional example. Also, the thermal protrusion of Example 2 whereinabout 30% of a total thickness of each of the upper shield and the lowershield is replaced by 46 wt % NiFe is reduced to about 80% of that ofthe conventional magnetic head. Further, the thermal protrusion ofExample 3 wherein about 70% of a total thickness of each of the uppershield and the lower shield is replaced by 46 wt % NiFe is reduced toabout 60% of that of the conventional magnetic head. Thus, the presentinvention is effective in reducing the flying height at room temperatureand largely improving the write/read characteristics, particularly, theresolution and the output noise ratio.

[0026] According to the above results, it is apparent that the effectivereduction of 15% or more in the thermal protrusion can be realized bysetting the ratio of the thickness of the magnetic material layer havinga low coefficient of thermal expansion to the sum of the thicknesses ofthe lower and upper shields to 30% or more.

[0027] In the present embodiment, the NiFe-based alloy is used by way ofan example of the magnetic material having a low coefficient of thermalexpansion. Coefficients of thermal expansion of NiFe-based alloys arelisted in FIG. 7-113 on page 342 of “Handbook of Magnetic Materials”which was published in 1975. The coefficient of thermal expansiondecreases gradually from the Ni content of 100% to reach 11.5×10⁻⁶/Kwhen the Ni content is 55% and then it decreases sharply with reductionin Ni content. The coefficient of thermal expansion starts to increasewhen the Ni content is 25% and then exceeds 11.5×10⁻⁶/K when the Nicontent is less than 30%. Accordingly, the thermal protrusion is largelyreduced by the use of the NiFe alloy having the Ni content of 30 to 55wt % as the magnetic material having a low coefficient of thermalexpansion of the present embodiment in accordance with the samecalculations as those used in Table 2. If the material having thecoefficient of thermal expansion of 11.5×10⁻⁶/K is used for the lowerand upper shields, it is possible to realize the effective reduction of15% or more in thermal protrusion as compared with the conventionalmagnetic head. The 15% reduction in thermal protrusion is obtainablefrom the calculation used for obtaining the results shown in Table 2.The effect of 15% reduction in thermal protrusion is such that thethermal protrusion in the conventional example of Table 2 caused by 50°C. of temperature rise is reduced by about 0.5 nm. In addition, thethermal protrusion in the conventional example of Table 3 is reduced byabout 0.7 nm. Table 3 will be described later in this specification. Inorder to reduce the thickness of the protection film, for example, onthe surface of the head by about 0.5 to 0.7 nm for the purpose ofreducing the flying height, it is necessary to carry out very difficulttechnology developments. Therefore, the reduction in thermal protrusiondescribed above is significantly effective in reducing the flyingheight.

[0028] While the magnetic material having a low coefficient of thermalexpansion is used for both of the upper shield and the lower shield inExample 1, it is possible to reduce the thermal protrusion by using themagnetic material for either one of the shields. Also, while the uppershield and the lower shield of each of Examples 2 and 3 are each thestack of layers, which consists of the layer of the magnetic materialhaving a low coefficient of thermal expansion and the 80 wt % NiFe alloylayer, it is possible to reduce the thermal protrusion by using thestack of layers for either one of the shields.

[0029] A structure of the stack of layers of the NiFe-based alloy havinga low coefficient of thermal expansion and the NiFe-based alloy having ahigh coefficient of thermal expansion is not limited to the two-layeredstructure. A three- or more layered structure or a layered structureconsisting of three or more layers of NiFe-based alloys having differentcoefficients of thermal expansion can achieve a reduction in thermalprotrusion similar to those described above.

[0030] Shown in FIG. 2B is a magnetic head having a lower shield and anupper shield each of which has a four-layered structure. Morespecifically, each of the lower shield and the upper shield is a stackof layers consisting of magnetic material layers 3 a and 6 a having alow coefficient of thermal expansion and 80 wt % NiFe alloy layers 3 band 6 b.

[0031] Thermal protrusions of a conventional magnetic head and thin filmmagnetic heads of the present embodiment were evaluated. The thin filmmagnetic head of the present embodiment shown in FIG. 2A was prototypedto evaluate the thermal protrusion thereof. The conventional magnetichead was manufactured such that it has the same structure as that shownin FIG. 1 and an upper shield and a lower shield are formed from 80 wt %NiFe. A thin film magnetic head of the present embodiment wasmanufactured such that it includes a lower shield lower layer 3 a of 46wt % NiFe alloy having a thickness of 1.1 μm, a lower shield upper layer3 b of 80 wt % NiFe alloy having a thickness of 1.0 μm, an upper shieldlower layer 6 b of 80 wt % NiFe alloy having a thickness of 0.5 μm, andan upper shield upper layer 6 a of 46 wt % NiFe alloy. The thermalprotrusion of each of the magnetic heads was evaluated by opticallymeasuring changes in shape of an air bearing surface caused by increasesin ambient temperature. Results of the evaluation are shown in Table 3.TABLE 3 Conventional Head Structure Example Example 4 Example 5 lowershield 80 wt % NiFe 46 wt % NiFe 46 wt % NiFe lower material 2.1 2.1 1.1thickness (μm) lower shield — — 80 wt % NiFe upper material 1.0thickness (μm) upper shield 80 wt % NiFe 46 wt % NiFe 80 wt % NiFe lowermaterial 1.3 1.3 0.5 thickness (μm) upper shield — — 46 wt % NiFe uppermaterial 0.8 thickness (μm) protrusion 0.9 0.40 0.65 amount (nm/10 C°)protrusion ratio 1 0.44 0.72 pass rate in 97.8 87.5 100 after-recordnoise test (%)

[0032] As shown in Table 3, the thermal protrusion of the thin filmmagnetic head of Example 4 wherein 46 wt % NiFe is used in place of 80wt % NiFe for forming the upper and lower shields is reduced to about40% of that of the conventional magnetic head. The thermal protrusion ofExample 5 wherein 46 wt % NiFe of an amount corresponding to 55% of thetotal thickness of the upper and lower shields is used in place of 80 wt% NiFe is reduced to about 70% of that of the conventional magnetichead. The lower pole front end layer 9, the lower pole back end layer10, the upper pole front end layer 12, and the upper pole back end layer13 of each of the experimental thin film magnetic heads are formed fromCoNiFe alloy. Therefore, the determined values of the amounts ofprotrusion shown in Table 3 are slightly larger than the calculatedvalues of the amounts of protrusion shown in Table 2. However, therelationship between the film thickness ratio of the 46 wt % NiFe alloylayer to the whole magnetic shield and the height of protrusion due tothe thermal protrusion in the calculated values is almost identical withthat in the measured values. In addition, it was confirmed that thereduction in thermal protrusion was achieved by using the magneticmaterial having a low coefficient of thermal expansion for the magneticshield in place of 80 wt. % NiFe having a high coefficient of thermalexpansion.

[0033] With regard to the prevention of increase in noise in readoutput, that is, another object of the present invention, noise inoutput waveform occurring after a write operation was measured. Noise inread out may occur due to the magnetic shield. This noise often occurssuch that when a write current is applied to a coil, a read magneticflux flows into the magnetic shield to change a magnetic domainstructure of the magnetic shield thereby causing the noise, in the shapeof a spike, in the read element. Such phenomenon is referred to as“after-record noise” in the present specification. In order to evaluatethe after-record noise, an after-record noise test was carried out insuch a manner that a magnetic head in which noise of 100 μV or higheroccurred 10 times or more after 5,000 times of application of the writecurrent was rejected so as to detect pass rates of the magnetic heads.Results of the test are shown in Table 3. Referring to Table 3, the thinfilm magnetic head of Example 4 having the magnetic shield formed from46 wt. % NiFe has a lower pass rate as compared with the conventionalexample; however, the thin film magnetic head of Example 5 having themagnetic shields each of which is the stack of layers consisting of the80 wt. % NiFe alloy layer and the 46 wt. % NiFe alloy layer has a passrate higher than that of the conventional thin film magnetic head. Thereason for the high pass rate has not been clarified, but it is presumedthat the stack of layers makes the magnetic domain structure less liableto change, thereby making the after-record noise less liable to occur.As described above, the present invention provides a thin film magnetichead that is capable of reducing the thermal protrusion and theafter-record noise.

[0034] In addition, the NiFe alloy mainly comprising 80 wt % Ni and thealloy mainly comprising 46 wt % Ni are used for the examination in theembodiments of the present invention. Each of the compositions of thesealloys may probably be changed in the range of about ±3 wt %; however,if changed, the same effect will be provided.

[0035] Apart from the crystal alloys such as the NiFe alloys, amorphousalloys are usable for forming the magnetic shield. Examples of theamorphous alloys may be CoTaZr, CoNbZr, and like alloys, each of whichmay have a low coefficient of thermal expansion depending on thecomposition thereof. However, it has been reported that the use of thesematerials increases the after-record noise in some cases. In addition,because of low thermal conductivity, these materials are not alwayspreferred from the standpoint of the reduction in thermal protrusion.

[0036] The present invention is basically applicable to the headstructure shown in FIG. 1 wherein the upper shield is separated from thelower pole piece. In the head structure having the integrated uppershield and lower pole piece, the after-record noise tends to occur ifthe 46 wt % NiFe alloy is used as the shield material, because the writeflux flows directly into the magnetic shield to change the magneticdomain structure.

[0037] The application of the present invention is not limited bystructures, such as a read element structure, a lower pole structure,and an upper pole structure, but the magnetic shield structure describedabove. For example, while FIG. 1 shows the thin film magnetic headincluding the lower pole front end layer 9, the lower pole back endlayer 10, the upper pole front end layer 12, and the upper pole back endlayer 13, the present invention is applicable to the following thin filmmagnetic heads. One is that a lower pole front end layer 9 and a lowerpole back end layer 10 are omitted and a lower pole front end is joinedto an upper pole front end layer with a write gap disposed therebetween.Another is that a thin film magnetic head in which a coil 15 is disposedbetween a lower pole front end layer 9 and a lower pole back end layer10 and an upper pole piece 17 has a flat surface. Yet another is that alower pole front end layer 12 and an upper pole back end layer 13 areomitted, a coil 15 is disposed between a lower pole front end layer 9and a lower pole back end layer 10, and a front end of a flat upper polepiece is joined to a lower pole front end layer with the upper polepiece being disposed on a write gap which is disposed between the upperpole piece and the lower pole piece. The present invention iseffectively applicable to the thin film magnetic heads having theabove-described write structures.

[0038] In the thin film magnetic heads of the present invention, the 46wt % NiFe alloy having a low coefficient of thermal expansion is usedfor forming the lower pole piece 8 and the upper pole piece 17 of eachof the write elements of the first and second embodiments. When the 80wt % NiFe alloy is used in place of the 46 wt % NiFe alloy for formingthe lower pole piece 8 having a thickness of 2 μm, the thermalprotrusion of the lower magnetic shield is 0.2 nm per 10° C. oftemperature rise, in accordance with the heat deformation calculationdescribed in the first embodiment. Further, if the upper pole piece 17having a thickness of 2 μm is formed from the 80 wt. % NiFe alloy, thethermal protrusion of the protection film 18 increases by 0.2 nm per 10°C. of temperature rise while the thermal protrusion of the lowermagnetic shield remains unchanged. Thus, in order to reduce the thermalprotrusion, it is important to use the magnetic material having a lowcoefficient of thermal expansion for forming the write element. It ispossible to provide the thin film magnetic head with decreased thermalprotrusion by using the 46 wt % NiFe alloy having a low coefficient ofthermal expansion for the lower pole piece 8 and the upper pole piece17.

[0039] In the thin film magnetic head of the embodiments, the writeelement is described as using the conventional longitudinal recordingtype element as shown in FIG. 1; however, if a vertical recording typewrite element is used as the write element as shown in FIG. 3 to writeand read data on and from the vertical medium, it is possible to achievethe same effects as those of the embodiments by adopting theabove-described configuration to the vertical recording type writeelement. In the case of using the vertical write element shown in FIG.3, the magnetic shields, the read element and the separation layer,which are denoted by reference numerals 1 to 7, are the same as thosedescribed above, while the lower pole piece 8 is used as an auxiliarypole piece and the main pole piece 21 is provided in place of the upperpole front end layer, thereby writing data on the vertical recordingmedium by use of the main pole piece.

[0040] In addition, it is possible to use a conventional CIP (readcurrent longitudinal application type) GMR element, a TMR element, and aCIP (read current vertical application type) GMR as the read element inthe embodiments. If any one of these elements is used as the readelement, it is unnecessary to change the configuration of the headelement to achieve the same effect. Further, the present invention isapplicable to a side shield type thin film magnetic head wherein each ofsides extending along the direction of the track width of the readelement is provided with a shield as shown in FIG. 4. Shown in FIG. 4 isthe read element and the magnetic shields as viewed from the air bearingsurface. In the present embodiment, the TMR element or the CPP GMRelement is used as the read element, and the read current is verticallyapplied to the read element. Therefore, the upper and lower shieldsserve also as electrodes for the read element 5. Denoted by 22 is aninsulation layer for the upper and lower shields. It is possible toimprove the read resolution in the direction of track width by providingeach of the sides of the read element with the side shield 23. If thelaminated film consisting of the layer of the magnetic material having alow coefficient of thermal expansion and the 80 wt % NiFe alloy layer isused for the magnetic shield in the present embodiment, the magneticshield is disposed in such a manner that the 80 wt. % alloy layer facesthe read element in the same manner as in FIG. 2A.

[0041] A disk storage device using the thin film magnetic head of thepresent invention can achieve the low flying height owing to thereduction in thermal protrusion. The present invention is particularlyeffective in ensuring reliability of a disk storage device, in a hotenvironment, which achieves a high recording density and a low flyingheight. In this case, the low flying height is a mechanical flyingheight of 20 nm or less from a surface of an extremely thin protectionfilm usually formed on an air bearing surface of a magnetic head to therespective surfaces of an extremely thin protection film and a lubricantlayer, both of which are usually formed on a surface of a recordingmedium.

[0042] As described above, it is possible to reduce the thermalprotrusion by using the magnetic material having a low coefficient ofthermal expansion of 11.5×10⁻⁶/K or less for the magnetic shield of thethin film magnetic head. Further, it is possible to provide the thinfilm magnetic head achieving reduced thermal protrusion and reducedafter-record noise by using a laminated film consisting of the 80 wt %NiFe alloy layer and the layer of the magnetic material having the lowcoefficient of thermal expansion for the magnetic shield.

What is claimed is:
 1. A thin film magnetic head comprising: a readunit, formed above a substrate, having a lower shield, a read elementand an upper shield; and a write unit having a lower pole piece, anupper pole piece, and a coil placed between said lower pole piece andsaid upper pole piece, said read unit and said write unit beingseparated from each other with a non-magnetic material; wherein amagnetic material having a low coefficient of thermal expansion of11.5×10⁻⁶/K or less is used for forming at least part of the lowershield or the upper shield.
 2. A thin film magnetic head according toclaim 1, wherein said magnetic material having low coefficient ofthermal expansion is a crystalline magnetic alloy.
 3. A thin filmmagnetic head according to claim 1, wherein said magnetic materialhaving low coefficient of thermal expansion is a NiFe alloy having acomposition comprising 30 to 55 wt % Ni.
 4. A thin film magnetic headaccording to claim 1, wherein each of said lower shield and said uppershield has a structure of a multilayer.
 5. A thin film magnetic headaccording to claim 4, wherein said NiFe alloy layer is used as a layer,except for layer closest to said read element.
 6. A thin film magnetichead according to claim 1, wherein at least one of said lower shield andsaid upper shield is a laminated film consisting of a layer formed fromsaid magnetic material having low coefficient of thermal expansion and alayer formed from a NiFe alloy having a composition mainly comprising 80wt % Ni, said 80 wt % NiFe alloy layer facing to said read element.
 7. Athin film magnetic head according to claim 6, wherein said magneticmaterial having low coefficient of thermal expansion is a crystallinemagnetic alloy.
 8. A thin film magnetic head according to claim 6,wherein said magnetic material having low coefficient of thermalexpansion is a NiFe alloy having a composition comprising 30 to 55 wt %Ni.
 9. A thin film magnetic head according to claim 6, wherein a ratioof a thickness of said magnetic material having low coefficient ofthermal expansion to a sum of thicknesses of said lower shield and saidupper shield is 30% or more.
 10. A thin film magnetic head according toclaim 9, wherein said magnetic material having low coefficient ofthermal expansion is a crystalline magnetic alloy.
 11. A thin filmmagnetic head according to claim 9, wherein said magnetic materialhaving low coefficient of thermal expansion is a NiFe alloy having acomposition comprising 30 to 55 wt % Ni.
 12. A thin film magnetic headcomprising: a read unit, formed above a substrate, having a lowershield, a read element, and an upper shield; and a write unit having alower pole piece, an upper pole piece, and a coil placed between saidlower pole piece and said upper pole piece, said read unit and saidwrite unit being separated from each other with a non-magnetic material;wherein a side shield is provide on each side of said read element, partof said side shield being formed from a magnetic material having a lowcoefficient of thermal expansion of 11.5×10⁻⁶/K or less.
 13. A diskstorage device comprising: a recording medium; a drive motor for drivingsaid recording medium; a magnetic head for reading and writing data fromand on said recording medium; a positioning mechanism for positioningsaid magnetic head; a first circuit system for controlling saidrecording medium, said drive motor, said magnetic head, and saidpositioning mechanism; and a second circuit system for supplying a writesignal to said magnetic head and processing a read signal from saidmagnetic head; wherein said magnetic head comprises: a read unit, formedabove a substrate, having a lower shield, a read element and an uppershield; and a write unit having a lower pole piece, an upper pole piece,and a coil placed between said lower pole piece and said upper polepiece, said read unit and said write unit being separated from eachother with a non-magnetic material; a magnetic material having a lowcoefficient of thermal expansion of 11.5×10⁻⁶/K or less used for formingat least part of the lower shield or the upper shield.
 14. A diskstorage device according to claim 13, wherein a flying height from anair bearing surface to said recording medium is 20 nm or less.